If you haven't already done so, brown the pork sausage until cooked through.
In a bowl combine cooked sausage, onion, stuffing mix, and the cheese.
Mix to combine.
Spray each cavity in a mini muffin pan with non-stick spray.
Add 1-2 tablespoons of the stuffing mix to each cavity.
In another bowl, combine the eggs and milk.
Whisk to combine and break up the eggs.
Add 1.5 tablespoons of the milk and egg mixture to each cavity.
Cover the mini muffin pan with foil and let sit at least 4 hours but preferably overnight.
Bake the breakfast Casserole Bites
The next morning, preheat oven to 350F.
Remove the pan from the refrigerator while the oven is preheating.
When the oven is ready, bake the breakfast casserole bites for 10 minutes while covered with foil.
After 10 minutes, remove the foil and cook for an additional 10 minutes.
When the breakfast casserole bites are done, remove from the oven and let cool for 1-2 minutes.
Remove from the mini muffin pan by running a knife around the edge of each breakfast casserole bite.
Notes
Spray the pan generously. Mini muffin tins have a lot of surface area and these will stick if you're stingy with the spray.
Drain the sausage well. Extra grease in the mix will make the bites greasy and can prevent the egg mixture from absorbing properly.
Keep the onion finely chopped. Larger pieces won't soften enough during the short bake time.
Don't overfill the cavities. Leave a little room for the egg mixture to puff up slightly as it bakes.
A disposable cup with a paper towel in the bottom is the best way to transport these if you're eating them on the go. Easy to carry, nothing to wash.
Double the batch and freeze half. They reheat fast and having them in the freezer means you actually have a portable breakfast ready on the worst mornings.